1. Field of the Invention
The present invention relates to a light source device and a projection display apparatus, and more particularly to a technology for minimizing damage caused when a high-pressure discharge lamp as a light source is burst.
2. Description of the Related Art
Projection display apparatus such as liquid crystal projectors and DLP (Digital Light Processing) projectors have recently been in widespread use. Generally, a projection display apparatus has a lamp as a light source, an image forming device for modulating light emitted from the lamp with an image signal, and an image optics for projecting image light that is generated by the image forming device onto a screen at an enlarged scale.
One conventional DLP projector having three digital micromirror devices (DMDS) is shown in FIG. 1 of the accompanying drawings. As shown in FIG. 1, the DLP projector has a light source comprising high-pressure discharge lamp 50 placed in metal lamp house 51 that is disposed in a main housing. Light emitted from high-pressure discharge lamp 50 is collected and guided by a reflector to travel through a predetermined light path to prism unit 52. The light applied to prism unit 52 is separated thereby into color lights in three primaries, i.e., red (R), green (G), and blue (B). Each of the separated color lights are then applied to the DMDs (not shown). The DMDs modulate the respective color lights and output the modulated color lights again to prism unit 52, which combines the color lights into image light. The image light is then projected by projection lens 53 onto a screen (not shown) at an enlarged scale.
The DLP projector also has a cooling fan 55 disposed in the main housing to-cool high-pressure discharge lamp 50. Cooling fan 55 delivers cooling air (ambient air) through inlet duct 56 into lamp house 51. After having cooled high-pressure discharge lamp 50, the cooling air is discharged through outlet duct 57 out of the main housing. High-pressure discharge lamp 50 is burst on rare occasions due to shocks, abnormal temperature rises, or individual lamp defects inherent in high-pressure discharge lamp 50. When high-pressure discharge lamp 50 is ruptured, the bulb thereof and the nearby reflector are broken up into pieces under the shock of the rupture, and the broken pieces tend to flow through outlet duct 57 and be ejected from the main housing. To avoid damage due to the ejected pieces, outlet duct 57 is designed to have a snake like shape with increased length and which incorporates therein three metal mesh filters 58 through 60 to prevent the broken pieces from being scattered out of the main housing. Details of the structure for preventing the broken pieces from being scattered out of the main housing are disclosed in Japanese laid-open patent publication No. 2003-202630 and Japanese laid-open patent publication No. 2004-294749.
Xenon lamps have a high internal bulb pressure of about 20 atmospheric pressures and a large volume. When they are burst, they are liable to release energy large enough to deform the metal lamp house which houses the xenon lamp therein. If the light source of a projection display apparatus comprises a xenon lamp, therefore, it is necessary to combine the xenon lamp with a more reliable and stronger structure for preventing broken pieces of the lamp from being ejected rather than instead of using other lamps as the light source.
The conventional proposal to use a longer outlet duct with metal mesh filters disposed therein is disadvantageous in that the cooling air cannot be discharged efficiently and has a reduced cooling effect, and the projector itself tends to become unduly large in size. In Particular, the longer outlet duct directly results in an increase in the size of the projector.